Recently, many advantageous features have been found in maltose and such recognition has led to the realization of an expansion of its uses. Thus, saccharified starch products wherein maltose is the predominant constituent are receiving great demands.
Conventionally, starch hydrolysates with a maltose purity in the range of 40-50%, w/w (all percents and parts will be given hereinafter by weight, dry solid basis or d.s.b. unless specified otherwise) have been obtained, by subjecting liquified starch to the action of malt amylase (a maltogenic enzyme). More recently, saccharified starch hydrolysates with a maltose purity more than 50% have become obtainable with relative ease by a combination of starch-debranching enzyme and beta-amylase.
In starch hydrolysates with a predominant maltose content prepared with conventionally-known maltogenic enzyme(s), for example alpha-amylase, beta-amylase and starch-debranching enzyme, however, maltotriose is formed necessarily. Further, since the maltotriose is substantially outsusceptible to such maltogenic enzyme(s), there was a limit to the increment of maltose purity. Investigations of the present inventors have shown that a conversion of the maltotriose, formed abundantly in the saccharified starch hydrolysates, into maltose is necessary to attain further maltose purity improvement.